A functional roller for use in electrophotographic printing often requires an outer surface layer of high electrical resistivity over a core of controlled electrical conductivity. U.S. Pat. No. 5,707,743; which is prior art to this invention; describes such a roller and a process of manufacture in which polybutadiene is incorporated in the materials of the core and the core is then baked to oxidize the polybutadiene at the surface of the core, resulting in a resistive surface on the core.
The embodiments of the foregoing U.S. Pat. No. 5,707,743 were for developer roller applications. A developer roller contacts a photoconductive surface and delivers toner to the photoconductive surface. This invention is for a modification of such developer roller embodiments to decrease the resistivity of the core and decrease the hardness of the final roller. Such a roller is consistent with being a developer roller, but the specific embodiment of this specification is a charge roller. A charge roller contacts a photoconductive member and is imparted with a high voltage, which thereby transfers an electrical potential to the photoconductive member. This voltage to the charge roller is typically an AC voltage overlayed onto a DC voltage, the peak AC voltage at least twice the DC being considered optimum for operation. This is a function which may be achieved by a corona discharge device and other known techniques, but contact charging, as with a charge roller, has the special advantage of creating minimal collateral discharges which can degrade the environment.
In accordance with this invention fillers are added to lower the electrical resistivity of the core. A polyether diol is added to lower the hardness and lower the resistivity of the core.